Modern tape measures (or xe2x80x9ctape rulesxe2x80x9d) typically include a coiled tape that is spring-biased towards associated retracted position. A housing generally surrounds and protects the tape and a retraction spring and includes an opening through which a distal end of the tape extends. Typically, the tape measure housing consists of two housing halves that are joined together by one or more screws. In addition, one of the housing halves typically includes an inwardly pointing integral post that provides an anchoring point for one end of the retraction spring. During assembly, a blade winding reel is placed over the post with the retraction spring engaged by the post, and the other housing half is then joined to the first housing half with the reel captured therebetween. During use, the distal end of the tape is pulled away from the housing; when released, the spring pulls the tape back into the housing so that the tape returns to the retracted position. The retracted tape is wound on the reel in the form of a convolute coil, with the reel rotatably supported by the housing.
One important consideration when designing commercially available tape measures is that the tape measure should be able to function even after being repeatedly dropped, as frequently occurs on a construction site. Dropping the tape measure subjects the tape measure to substantial shock loadings that sometimes lead to the retraction spring becoming pinched or otherwise misaligned with respect to the anchoring post, quickly rendering the tape measure unusable.
Another consideration in designing tape measures is that the presence of dirt and other contaminants inside the housing may tend to degrade the performance of the retraction mechanism, by adding friction, increasing wear, and other mechanisms. However, providing a completely sealed housing is impractical, particularly given the need to pay out the tape measure blade in a convenient manner and the extreme cost pressures present in the marketplace.
Accordingly, there remains a need for improved tape measure designs, particularly those that have a more robust design, an preferably designs that address one or more of the problems outlined above.
The present invention is directed to a power-return tape measure, and/or a method of assembling a power-return tape measure, that employs a distinct internal retainer to help keep a retraction spring in the proper position relative to its anchoring post.
In one embodiment, the tape measure comprises a main case having first and second sidewalls and a peripheral wall extending between the sidewalls. A tape measure blade is coiled about a drum assembly in a conventional fashion. Also as is conventional, the drum assembly includes a drum having side flanges disposed generally parallel to the main case sidewalls and a core therebetween. The core of the drum generally defines a central cavity. The drum assembly further includes a drum cap secured to the drum so as to substantially enclose the central cavity. The drum assembly also includes a disc disposed internal to the central cavity and adjacent the drum cap. The drum cap has a first hole of a first diameter and the disc has a second hole of a second diameter smaller than the first diameter. The disc may be metallic and should have a periphery radially larger than the first hole. The power-return retraction spring is wound substantially or entirely within the central cavity and mounted to a post so as to provide a retraction bias for the tape blade. The post may include a slot, with the spring mating to the post via the slot. The post is disposed between the first and second sidewalls and extends through the central cavity, the first hole, and the second hole. The post extends through the second hole with a sliding fit and through the first hole without touching the drum cap. For example, the post may be spaced from the edge of the first hole so that there is a uniform gap therebetween. At least one of the sidewalls may include an inwardly pointing boss that cooperates with the first hole to provide a rotational bearing surface for the drum assembly. The other sidewall may also have a boss that cooperates with other features of the drum assembly to provide another bearing surface on the other side of the drum.
In another embodiment, the tape measure may comprise a tape measure blade coiled about a reel, the reel having an interior central cavity. A post extends through the central cavity. A spring is wound substantially or entirely within the central cavity and mounted to the post so as to provide a retraction bias for the tape blade. A cap is secured to the reel so as to substantially enclose the central cavity and the spring. A retainer is disposed between the spring and the cap. The retainer is distinct from both the reel and the cap and may advantageously be metallic and disc shaped. The cap has a first hole of a first size and the retainer has a second hole of a second size smaller than the first size. The post extends through the second hole with a sliding fit and through the first hole in spaced relation to the cap. The post should rotationally fixed relative to the main case. The post and the retainer substantially close off the first hole. A main case substantially encloses the reel.
In another embodiment, a method of assembling a tape measure includes providing a main case having a boss thereon; providing a reel having a central cavity; providing a tape measure blade convolutionally wound on the reel; providing a post having a slot therein; anchoring a spring to the post via the slot, the spring disposed substantially within the central cavity and operative to bias the blade towards being wound on the reel; providing a retainer having a first hole therein, the first hole sized to slidably engage the post; placing the retainer over an end of the post and moving the retainer toward the spring; capturing the retainer in the central cavity between the spring and a cap connected to the reel, the capturing including positioning the cap so that the post extends through the second hole therein in spaced relation to the cap; rotationally supporting the reel for rotation relative to the housing via the boss and second hole; and substantially enclosing the post, the reel, the spring, the retainer, and the cap in the housing. The main case may have distinct first and second case portions, with the first case portion including the boss.